Randomized, placebo-controlled, and crossover design study explored the associations among MBG excretion with systolic BP and aortic pulse-wave velocity across conditions of 5 weeks of a low-sodium (77 9 mmol/d) and 5 weeks of a normal-sodium (144 +/- 7 mmol/d) diet in middle aged/older patients (eight men and three women; 60 +/- 2 years) with moderately elevated blood pressure (139 +/- 2 / 83 +/- 2 mm Hg). Urinary MBG excretion (weekly measurements; 25.4 +/- 1.8 vs. 30.7 +/- 2.1 pmol/kg per day), systolic BP (127 +/- 3 vs. 138 +/- 5 mmHg), and aortic pulse-wave velocity (700 +/- 40 versus 843 +/- 36 cm/s) were lower during the low- versus normal-sodium condition (all P<0.05). Across all weeks, urinary MBG levels were related to systolic BP (slope=0.61, P<0.001) and sodium excretion (slope=0.46, P<0.001). These associations persisted during the normal- but not the low-sodium condition (both P<0.005). MBG excretion also was associated with aortic pulse-wave velocity (slope=0.70, P=0.02) and endothelial cell expression of NAD(P)H oxidase-p47phox (slope=0.64, P=0.006). These results show, for the first time in humans, that dietary sodium restriction reduces urinary MBG levels and that urinary MBG excretion is positively associated with systolic BP, aortic stiffness (aortic pulse-wave velocity), and endothelial cell expression of the oxidant enzyme NAD(P)H oxidase. Importantly, MBG excretion is positively related to systolic BP and aortic stiffness, a major feature of cardiovascular aging, over ranges of sodium intake typical of an American diet.